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<p>Dear Federico</p>
<p>Thanks for your detailed response. I would look meet prof.
Seymour Cahangirov. I actually, have recently joined Bilkent, so
do no know many people yet. <br>
</p>
<br>
<div class="moz-cite-prefix">On 09/17/2016 04:41 PM, Federico Iori
wrote:<br>
</div>
<blockquote
cite="mid:1532450390.2092500.1474112477856.JavaMail.zimbra@u-psud.fr"
type="cite">
<div style="font-family: arial,helvetica,sans-serif; font-size:
12pt; color: #000000">
<div>Hi.<br>
</div>
<div><br>
</div>
<div>In my opinion, I think the approach you chose depends
strictly from the question you want to answer and after that
from the the size (number electrons, Number plane wave thou)
you have.<br>
</div>
<div>Do you need a full excitonic optical spectrum ? or just a
RPA spectrum is sufficient for your study?<br>
</div>
<div><br>
</div>
<div>If it is silicon-like and then maybe not too much
computationally demanding, I think you can use a linear
response TDDFT as a first step and then move to a more
sophisticated approach as GW (to calculate not the optic, but
the screening of your material) + Bethe-Salpeter equation BSE
to have correctly acces to the excitonic effects in your
absorption spectra.<br>
</div>
<div><br>
</div>
<div>Of course all the calculations have to be converged wrt
kpoints, number of Gvectors, number of bands. When increasing
these parameters wrt their pristine value for your converged
density in the DFT framework the computational cost will
increase not linearly.<br>
</div>
<div><br>
</div>
<div>I would suggest you to have a look and to do the tutorial
with the Yambo code on a small system as they proposed in
order to correctly understand what are you doing.<br>
</div>
<div><br>
</div>
<div>Moreover there is the theory to have a look at in order to
understand the meaning and the effect of the quantities you
are calculating .<br>
</div>
<div>I would reccomend especially<br>
</div>
<div>Onida Reining Rubio Rev Mod Phys 2002 <a
moz-do-not-send="true"
href="http://journals.aps.org/rmp/abstract/10.1103/RevModPhys.74.601">http://journals.aps.org/rmp/abstract/10.1103/RevModPhys.74.601</a><br>
</div>
<div>as all the others references in the yambo website as well.<br>
</div>
<div><br>
</div>
<div>Moreover, since I notice you are in Bilkent UNiv, try to
ask to Seymour Cahangirov from the same univ. I think he can
address you properly.<br>
</div>
<div><br>
</div>
<div>I hope this could help a bit.<br>
</div>
<div><br>
</div>
<div>With the best<br>
</div>
<div>Federico<br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
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<div><span style="font-size: 10pt"
data-mce-style="font-size: 10pt;"><b>Federico IORI</b></span></div>
<div><span style="font-size: 10pt"
data-mce-style="font-size: 10pt;">Marie Curie
Fellow<br>
Laboratoire de Physique des Solides<br>
Bâtiment 510 - Rue André Rivière<br>
91400 Orsay</span></div>
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data-mce-style="color: #000; font-weight: normal; font-style:
normal; text-decoration: none; font-family:
Helvetica,Arial,sans-serif; font-size: 12pt;"><b>De: </b>"Muhammad
Adnan Saqlain" <a class="moz-txt-link-rfc2396E" href="mailto:saqlain@bilkent.edu.tr"><saqlain@bilkent.edu.tr></a><br>
<b>Para: </b>"pw forum" <a class="moz-txt-link-rfc2396E" href="mailto:pw_forum@pwscf.org"><pw_forum@pwscf.org></a><br>
<b>Enviados: </b>Sábado, 17 de Septiembre 2016 13:25:12<br>
<b>Asunto: </b>[Pw_forum] calculation of absorption spectrum<br>
<div><br>
</div>
Dear users<br>
<div><br>
</div>
I have a system consisting of 94 atoms (periodic with cell
lengths of <br>
16.5, 8.5 and 8.7). I want to calculate its absorption
spectrum. Can <br>
anyone guide me which technique would be easy to run.
Actually, we have <br>
16 core machine and we can run a job for a maximum of 15 days
only. <br>
Based upon this time limit, I would like to know which
technique would <br>
be suitable. TDDFT or GW?<br>
<div><br>
</div>
any help in this regards would be highly appreciated.<br>
<div><br>
</div>
Thanks<br>
<div><br>
</div>
Adnan<br>
<div><br>
</div>
Bilknet U. Ankara<br>
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